Automatic switch for use in telephone or like systems



13. 1940- c. E. BEALE r AL 2,210,816

AUTdMATIC SWITCH FOR USE IN TELEPHONE 0R LIKE SYSTEMS Filed March 2,. 1933 z sheets she z 2.

.C l'mmm To CALL O '0 STORING l 3 EQUIPMENT M luvs/wens CHARLES EDMUND BEALE g TDRIS TREVOR RICHARDS A TY,

Patented Aug. 13, 1940 UNITED STATES.

AUTOMATIC SWITCH 'FOR IN TELEPHONE OR LIKE SYSTEMS Charles Edmund Beale and'ldris Trevor Richards,

' Liverpool, England, assignors to Associated Telephone & Telegraph '(lompanmchicago, 111., a corporation of Delaware Application March 2 1938, Serial NoL193A14 In Great Britain March 10, 1937 10 Claims. (Cl. 179-457) The present invention relates to telephone systems and automatic switches suitable for use therein and is more particularly concerned with arrangements for theselection of trunk lines in automatic'trunk exchanges. The invention is moreover particularly concerned with group selector switches of the so-called two-digit type, that is, requiring the transmission of two digits to complete their operationand preferablythese switches operate on the longitudinal and rotary principle. I 1

In exchanges of the kind contemplated where automatic switches are used for selecting trunk lines, the operator usually keys upthe routing 5- digits required into a keysending equipment which thereupon sets up the automatic switches. In a-known arrangement of this type the switches which have direct access to-the trunk lines are of the two-digit vertical and rotary type so that in an exchange employing first, secondand third selectors, the third digit keyed by on operator will cause a third selector to step vertically to select a level on 'whichis situated, the required group of trunks; In response to the keying of l as a fourth digit the switch wipers are advanced into engagement with the first set of outlets in the level selected. The first outlets of each level are not connected to a trunk but are wired back into the switch so that if the switch wipers are set thereon by a single-impulse a relay in the switch is operated to initiate the rotary hunting operation over the group of "nine trunks connected to the remaining nine outlets of the level. One object of theinvention is to provide a means whereby these first outlets may be utilised for connection to trunks; thereby .extendingthe'c'apacity of trunk groups from nine to ten trunks. In the prior arrangement if all outlets in the trunk group are engaged. thewipers are rotated to the 11th position and the call is placed in storage. When a trunk in the required group becomes free the operator is signalled from the call .storing "equipment and she may then cause the third selector to restore to the rotary normal position and then re-(sea'rch the level. Another object of theinvention is to provide the switch with further facilities whereby it may also perform a hunting operation overa sub-group of highgrade trunks in a main group of trunks and whereby if all outlets in either. the main group or the sub-group are tested and found to be engaged the operatormay cause the switch to restore from the end of. either of. these groups and re-searchthe whole maingroup.

According to one feature of the invention a telephone system including a group selector switch is arrangedso that initiation of the hunting movement after the group selecting movement has'taken place is dependent on the receipt by the switch of a signal different from those effecting the movement of the switch which signal results from a specific operation at the calling point.

According to another feature of the invention in a group selector switch for use in telephone or like systems after unsuccessful hunting for an idle line in a grOup has taken place the switch is adapted to hunt over a difierent group in response to a control signal from the calling point. I

According to another feature of the invention it group selectorswitchfor use in telephone or like systems after unsuccessful hunting for an idle line in'a group has taken place the switch is adapted to hunt again over alarger group of li es including the lines of the original group.

According to a further feature of the invention in a group selector switch'for use in telephone or like systems after unsuccessful hunting for an idle line in a group has taken place a busy signal is transmitted back in a circuit independent of the switch wipers which signal is adapted to be removed by anfoperation at the, calling point without the ,position ofthe switch wipers being changed. i I

The invention will be better understood from the following description of one method of carrying .it into effect, reference being had to the accompanying drawings comprising Figs. 1 and 2 whichwhen arrangedside by side form a circuit diagram of a 100-outlet two-digit group selector which is suitable for use in an automatic trunk exchange. 1 y I The switch is of the two-directional type and hasso-called rectangular movement in that no release magnetisprovided, the restoration of the switch 'to normal being effected by stepping the wipers forward to the end of the level and then allowing them to com'pletetheir restoration by a vertical and rotary movement.

Forthe purpose of thedescription the selector is as'sumed'to be used asla third trunk selector and has access to ten groups of ten trunklines each, one such group being accommodated on each level. It will further be assumed that the originating operatorat an automatic trunk board desiresaccess toa. trunk group on level 3 of the switch, this main group including a sub-group of five high grade trunks which are located on outlets 6 to 0 of the level.

When the switch is seized from'the preceding second trunk selector, the loop extended forward over the negative and positive conductors from an impulse sender which is temporarily associated with the operators keyset during the setting up of the connection operates relay A and battery potential extended from the operators position circuit over the S lead operates relay CS by way of its upper winding. Relay GS thereupon at armature csl connects earth from the off-normal contacts N3 to operate relay B which on operating, at armature bl locks independently of the contacts N3 and at armature 02 applies a guard earth to the incoming P conductor. Relay C is also operated over its right-hand winding by way of armature b6 and resistance Y6 and at armature cl it prepares an impulsing circuit to the vertical magnet VM by way of armature al and the left-hand low resistance winding of relay C. Although relay DF is in series with the operating windings of relayA it is non-operative under the above condition by reason of the differential arrangement of its windings and for this reason also it has no effect on the response of relay A to subsequent trains of impulses.

"When the first train of three impulses is received in response to the keying up by the operatorof the third digit 3 in the number, relay A responds and on each release of this relay earth is extended over armatures bl, csl cl, (1M and al, left-hand low resistance winding of relay C, armature 65, contacts NR3, magnet VM tobattery and accordingly the switch wipers are raised to the desired level 3. On the first vertical step the off-normal springs are mechanically operated and at contacts N3 earth is extended over armature h3, contacts NR2 and armatures e2 and 116 to short-circuit the right-hand energising winding of relay C so that this relay willremain held during the impulse train on its left-hand winding but will release a short interval after completion of the train. v

Assuming now that the operator wishes to gain access to any one of the group of ten outgoing trunk lines on this level, she will have keyed up I as a fourth digit. In response tO' thekeying of this particular digit the sender transmits .a special signal immediately after the end of the third digit for instance as described in British Specification No. 10,54 37. Thissignal momentarily unbalances the incoming loop to relays DF and A for example by the connection of earth potential thereto so that the differential relay DF now operates while relay A remains held on its upper winding. Relay DF at armature dfl operates relay TA over its middle Winding and this relay thereupon locks temporarily over its left-hand Winding in seriesJ-with armature tal, off-normal contacts N2, rotary magnet interrupter contacts rm and armature M3 to earth. At armature ml the short-circuit is now removed from the left-hand winding of relay AR which operates in series with the middle winding of relay TA while at armature 150.2 the right-hand winding of relay TA is connected to the test wiper P in preparation for testing for a free outlet. Relay AR upon operating, at armature ar5 locks over its right-hand winding in serieswith resistance YB, at armature ar3 provides an additional short-circuit to the right-hand energising winding of relay C and at armature ar4 disconnects the impulsing circuit extending tothe rotary magnet RM. On the release of relay C, a

self-interrupted driving circuit is completed for the rotary magnet RM from earth, armature ta3, interrupter contacts rm, contacts N2, armatures 04, H4 and hi, magnet RM to battery. On the first energisation 0f the magnet RM, the wipers are advanced into engagement with the first set of contacts in the'level selected whereupon the rotary oiT-normal springs NR are mechanically operated and also the magnet interrupter contacts rm are opened.

If the test wiper P encounters an engaged outlet, that is, one marked by the presence of earth potential, relay TA will be maintained operated on its right-hand winding and the disconnection of the holding circuit over its left-hand winding by the contacts rm is therefore without efiect. However the rotary magnet RM releases and when the interrupter contacts again close the magnet is again energised to advance the wipers to the next set of contacts. This stepping operation continues automatically until either a free trunk line in the selected group is found or alter natively the wipers are rotated to the l lth position where the call is placed in storage.

Assuming first that a free outlet is encountered, there will be no earth potential extended over the P' wiper to hold relay TA operated when the interrupter contacts rm open and this'relay therefore quickly restores and at armature ta3 opens the magnet driving circuit and at armature m2 immediately guards the outlet seized by extending earth over armatures b5, a1! and M2 to the P wiper. A circuit is now completed from earthfarmature b5, windings of relays HX and H in series, armatures M2, M5 and M2, magnet RM to battery in order to operate both of these relays, the magnet RM being non-operative in this condition, Whilst at armature ta6 relay C is re-operated due to the removal of the shortcircuit from its right-hand winding. Relay HX at its armatures hxl to hxB switches the incoming leads through to the seized outlet comprising a trunk relay set, one of which is providedfor each trunk line, and also at armature it disconnects relay CS which releases and opens the holding circuit of relay B. On the operation of relay C the incoming P lead is also extended through over armatures c2 and 714 and during the release time of relay B a guard and hold earth is maintained on the P conductor until an earth is returned from the trunk relay set. Re-

operates and at the same time they complete an:

operating circuit for relay SR which thereupon at armature sr2 disconnects the operating circuit for relays H and HX, this circuit being normally completed on release of relay .TA, so that these two relays fail to operate and consequently relays CS, B and AR remain operated.

It will be understood that the multipled l lth contacts on all levels of the banks PS and S extend over pairs of common leads such as [2 and [3 to call storing equipments, one of which is provided for each group of trunks. Each call storing equipment serves to display the number of calls awaiting idle trunks in the associated group and gives facilities for automatically putting the trunk group into delay when any predetermined number of calls are waiting. 'When -a trunk line in a group becomes free, the associated call storing equipment signals all operators waiting for that line and they, in a manner to be described, cause the release of the trunk selector to which they are connected, and it then,

relay TF to the S wiper in preparation for the reception of a trunk free signal. The release of relay TA also completes a circuit for relay G from earth, armature b l, contacts N3, armature h3, contacts NR2, armatures m4, hs3 and \e4,.upper winding of relay G to battery. Accordingly-at armature g3 a busy tone transformer is connected up over common lead ID to the lower winding of relay A whereupon busy tone is applied by induction through the upper two windings of this relay to the incoming speaking conductors in a balanced circuit and thence is transmitted to the operator.

The operator on receiving busy tone may remove it by operating the non-locking ring call key of the connecting circuit involved theefiect or" which is to unbalance the incoming loop 'so thatrelay DF is again operated. Relay DF at armature dfl re-operates relay TA from earth, armature bl contacts N3, armatures srl, dfl and middle winding of relay TA to battery and this relay thereupon locks over its left-hand winding by way of armatures tal and ta3. At armature tall relay G is now released and at armature-g3 it opens the busy tone'circuit to the operator. The connection is retained in order to await a trunk free signal from the associated call storingequipment but in the meantime the operator may attend to other calls.

As soon as a trunk in-the-required group be comes free, interruptedearth potential is fed back-"over common lead l3 and the S wiper to effect the intermittent operation of relay TF and similar relays in any other third trunk selectors which are awaiting an idle trunk in the group. Each time relay TF operates the low resistance earth normally applied to the incoming S lead over the upper low resistance winding of relay CS isreplaced at armature tfl by a high resistance earth comprising the two windings of'relay CS in series'and this brings about the release-of a relay connected to the S lead in the operators connecting circuit which in turnfiashes the supervisory lamp in place of the normalsteady glow..

The operator may now cause the trunk selector to release-to its rotary normal position and research the level, by operating her funlock-call key which is of the non-locking type. On the operation of this key positivebattery is applied to the S lead so that rectifier MRB now becomes conducting and enables relay RL to operate over its left-hand winding. RelayRL at armature TI! releases relay SR which at armature sr2- again prepares an operating circuit for relays H and HX and at armatures sr3 and srd removes re sistance YD and relay TF from the wipers PS and S respectively. Armature rll also short-circuits relay C which releases in order to prepare'anem ergising circuit for the vertical magnet VM, while at armature 1'22 the right-hand winding of relay TA is disconnectedfrom the P wiper and at armature 1:13 relay TA'is maintained over its middle Winding in series with the left-hand winding of relay AR. At armature 1'14 an ,energising circuit iscompleted for the vertical magnet VM is follows: earth, armature'ta3, contacts rm and N2, armatures c4 and T14, low resistance right-hand winding of relay RL, rotary oil-normal contacts NR3, magnet VMto battery.

I The vertical magnet pawl when operated is arranged. to engage with an extension arm of the rotary det'ent and move it out of engagement'with the rotary ratchet member so as to initiate the rotary release of the wipers along the path over whi'ch they have been set, for instance in. the manner described in' Patent No. 2,028,689.

When the wipers reach their rotary normal positionythe vertical ratchet member re-engages with the vertical holding detent thus preventing further release of the wipers to their fully restored position. In this position the rotary ofinormal springs are restored while at the commencement of the release operation the 11th step cam springs are also restored and at contacts SI maintain a 'short-circuiting earth on relay C in preparation for re-search of the level. The restoration of contacts NR3 releases the vertical magnet VM and opens the holding circuit of relay 'RL. This relay upon releasing reconnects the winding of relay TA to the P wiper at armature r12, disconnects the middle winding of 'relay TA at armature 113 and at armature r24 completes -a--self-interrupted driving circuit for the rotary magnet RM-so that re-search of the group now takes place in the same manner as the initial search.

3At' the end of the conversation the operator throws her release key on reception of the clearing signals on'her call and answering supervisoryflampsand in response to this operation teh trunk relay set removes the hold earth from the Plead thus bringing about the release of'relays I I and HX. Relay H thereupon at armature h2 opens-the circuit of relay C and when this releases a self-interrupted driving circuit is'completed for'the rotary magnet RM as follows:-

earthed delayed alarm equipment, common lead I [,test jack springs T, armatures b3, 01 and tall,"

contactsi andNZ, armatures 04, TM and hl, magnet RM to battery; The wipers areaccord ingly advanced'tothe 12th position whereupon they 'restore 'verticallyfunder gravity and then rotate under spring control under the banks to their full 'normal position where the off-normal contacts N2 open the magnet energising circuit. A momentary unguard interval comprising the sum of the release times of relaysI-Iand C is provided-catheincoming P lead to allow preceding switchesto release With a minimum of delay. On release of relay C the guard earth is replacedjovercontacts Ni and armature 02 until contacts NI open when the switch reaches normal.

- Considering new the case in which the operator tures- 713, ar3, list and c3, lower winding of relay CR," contacts NR3, magnet VM to battery whereupon relay CR operates but the magnet VM' does not. At armature crl a circuit is now completed for relay E and on operation of this relay it looks up independently of armature crl at armature 'e-l, at armature e5 prepares an impulsing circult for the rotary magnet RM and at armature e2 removes the short-circuiting' earth from the right-hand winding of relay C which then reoperates. Relay CR now remains held over its upper winding by way of armatures GT2, al, (114, cl,.csl and bl since its lower winding is disconnected at armature c3.

In response to the keying of the fourth digit a train of six impulses is transmitted from the sender and relay A again responds. On each release of relay A earth is extended via the lefthand winding of relay and armatures 65 and hl to energise the rotary magnet RM so that the wipers are rotated to the desired position. Due to its slug relay CR remains operated over its upper winding during the train of pulses, while relayC also holds up since itsright-hand winding is short-circuited on the first rotary step at contacts NR2 and armature e2.

At the end of the train of pulses relay C restores after a short interval and at armature Cl opens the holding circuit of relay CR which commences to release slowly. At armatures c and W3 relayi-IS is now connected to the Pl wiper during the release time of relay CR and since the Wipers have been positioned to the first outlet of the sub-group,- relay HS will operate on its' upper winding in series with a resistance battery potential connected to the first outletof the groupon the Pl bank. Relay HS locks over its lower winding by way of-armatures yl, 7184, M3 and b3 and at armature hs5 prepares a further energising circuit for the rotary magnet Since relay E is now operated the release of armature 06 connects an earth to relay TD. If the first trunk in the sub-group is found to be free, relay TD operates in series with resistance YB since there will be no busying earth extended back over the P wiper and metal rectifier MBA in a conductive direction to prevent its operation. Relay TD thereupon at armature td2 operates relays H and BK which switch the lines through in the normal manner while at armature tdl a guard earth is extended from armature 115 on to the outlet seized. Relays H and HK on operating reoperate relay C by removing the short-circuit at armature 713 and release relays A, CS and. B in the normal manner and at armature c6 relay TD is released and the P lead is extended through over armatures c2 and 714.. On the release of relayCR after its slow release period, relay I-IS releases since its lower winding is disconnected at. armature b3 and relay E also releases. The circuit conditions during conversation are now as before described.

Ifthe first ,trunk in the sub-group is engaged, an earth is. extended over the P wiper and rectifier MRA to shunt relay TD and prevent its operation. On the release of relay CR the energising circuit for relay E is disconnected since relay HS is now operated and on the release of relay E the short-circuit is removed from relay Cat armature e2. Relay C now re-operates and at armature 06 it extends earth over armatures 92, 7155 and hi to energise the rotary magnet,

interrupter contacts rm and armatures hs2, hsi and e4 to operate relay G on its upper winding. At armature gl earth is extended by way of the lower winding of relay G to the winding of relay TD while the lower winding of relay HS is disconnected but this relay remains held operated for a further short interval due to its slug. Moreover at armature g2 the rotary magnet circuit is opened and the magnet restores and opens the energ'ising circuit of relay G over its upper winding at contacts rm. If this second outlet in the subgroup is also busy, relay G now releases since the earth extended over the P wiper prevents it holding on its lower'winding in series with the winding of relay TD. On the release of relay G a circuit is again completed for relay HS at armature gl' by way of its lower winding, this relay having been held operated during this time due to its slug; while at armature 92 the magnet RM is again energised. Interaction between relay G and the magnet RM continues until a free outlet in the sub-group is reached, or alternatively the wipers are rotated to the last outlet in the subgroup.

When a free outlet is reached, relay G holds in series with relay TD which operates and energises relays H and HX as before. On operation of relay H relays G and TD are released at armature b3, and relay HS also releases after its slow period.

If all outlets in the sub-group prove to be busy, when the wipers reach the last of these outlets relay G holds operated over its upper winding, armatures e4 and M3, high resistance YE, armature 05, Pl wiper and bank to an earth which marks the last line of the sub-group. On the release of relay I-IS after its slow period, relay G remains held over its upper winding, armatures e4, hs3 and m4, contacts NR2, armature 3, contacts N3, armature bl to earth and accordingly busy'tone is returned to the operator over armatures g3 and hsl.

The operator on finding that all high grade trunks in the sub-group'are busy may decide that an ordinary trunk in the group may be utilised to complete the connection and she therefore again operates her unlock key to bring about the operation of relay RL. The switch now restores to the rotary normal position and then re-searches the whole group of trunks on the level in the manner previously described.

Facilities are also provided whereby the operator may select any particular trunk of a group except the first of a main group or the first of a sub-group therein, and if this trunk is found toibe busy, no hunting takes place but the switch camps on the trunk until it becomes free. Generally the above facility is'likely to be required whenever an operator is setting up an exceptionally long distance call when it is important to utilise the highest grade trunk line available. Considering now the circuit operation, on the completion of the train of rotary setting pulses, relayC restores and opens the holding circuit of relay GR in the normal manner. Relay HS is connected as before to the Pl wiper but since the wipers have not been positioned to the first line of thesub-group, relay HS cannot operate. Earth is also connected at armature c6 to relay TD which operates in series with resistance YB if the selected trunk is free and the operation proceeds in a normal manner. If the selected trunk is busy however, the earth potential encountered by the P wiper .;will prevent relay TD from operating. Relay CR releases after a short interval but relay E now remains held over armatures el, hs i, (M3 and n3, contacts N3 and armature b l to earth. An earth is therefore maintained on the left-hand terminal of relay TD over contacts NR! and armature c6 and c3 and the switch wipers will remain on the selected outlet until it becomes free, when relay TD operates and operates relay H and HK to switch the connection through. When this occurs the operator is signalled in the normal manner by the darkening of her supervisory lamp due to the changeover from a low resistance earth normally extended on to the S lead by way of the upper low resistance winding of relay CS to a high resistance earth connected to the S lead by way of a high resistance relay in the trunk relay set associated with the selected trunk.

Leads NA and NE and resistance YA are utilised in connection with the inclusion of thermionic repeaters, resistance YA serving as a line balancing arrangement during the setting of the switch.

Rectifier MIRA is provided to prevent an earth by way of the winding of relay TD from being extended on to the P wiper during the camp-on period, which would influence other switches connected to the same outlet.

We claim:

1. In a telephone system, a selector switch having access to groups of lines and controlled over a calling subscribers line by signals of one character to operate the switch to elect a group of lines, means in the switch operated before the switch is released responsive to a signal over the calling subscribers line diiferent from that used to directively operate the switch for initiating a hunting movement of the switch to select an idle line in the selected group.

2. A selector switch having access to groups of lines and controlled over an incoming line to elect a group of outgoing lines and operated thereafter to hunt for an idle line in the elected group, and means in the switch operated in response to a control signal over the incoming line before the switch is released to cause the switch to hunt over a different group of outgoing lines after an unsuccessful hunt over the selected group.

3. A selector switch as claimed in claim 2 in which the second group over which the switch hunts also includes the first group.

4. A selector switch as claimed in claim 1 in which the signal for initiating the hunting operation consists of an unbalanced condition of the circuit extending from the calling line to the switch.

5. A selector switch as claimed in claim 2 in which there is a differential relay in the switch operated by the control signal to cause the switch to hunt over said different groups.

6. A selector switch as claimed in claim 1 in which there is a differential relay in the switch :operated by said control signal to initiate said hunting operation 7. A selector switch having access to groups of lines and controlled over a calling subscribers line to elect a group of lines and then hunt for an idle line in the elected group, means in the switch operated in response to a special control signal from the calling line to initiate said hunting operation, means for returning a busy signal to the calling subscriber in case all the lines are busy, and means in the switch operated in response to said special control signal after an unsuccessful hunting operation to remove the busy signal without releasing the switch to normal.

8. In a telephone system, a selector switch having access to groups of lines, means for operating the switch to elect a group of lines and to then select an idle line in the elected group, and means in the switch controlled solely over the calling subscribers line for causing it to hunt over a different group than that first tested after an unsuccessful hunt for an idle line in the elected group and while the switch is maintained partially operated.

9. A selector switch as claimed in claim 8 in which there is means for directing the switch to the first line of a selected portion of the first group to thereby cause hunting only over that portion in the first instance.

10. A selector switch as claimed in claim 8 in which there is means for directing the switch to a line in the group other than the first to prevent hunting operations and give a busy signal in case that particular line is busy.

' CHARLES EDMUND BEALE. IDRIS TREVOR RICHARDS. 

